Tea is one of the most widely consumed beverages in the world, besides water. It is generally consumed in the form of black, oolong or green tea which originates from Camellia sinensis grown mainly in China and Southeast Asia. Black tea is consumed mainly in Western and some Asian countries and green tea is consumed predominantly in China, Japan and India.

Tea was first used as a medicine in Southwest China 5000 years ago. Between 1100BC and 200BC, drinking tea was recommended to maintain health. By the Tang Dynasty (AD618-907), tea became an object of veneration and the tea trade inside China flourished. Since then, drinking tea has become an important part of Chinese culture and is still regarded as an important part of health maintenance. Green tea is produced in most areas of China and is the most popular category of tea. Representative varieties include Dragon Well (Long Jing) and Biluochun from Zhejiang and Jiangsu Provinces respectively

Green tea is made from freshly picked tea leaves which go through heating and drying processes, but not fermentation like black tea varieties. This enables the leaves to keep their original green color and retain most of its natural substances like polyphenols and chlorophyll contained within the leaves.

According to Traditional Chinese Medicine (TCM) understanding, tea has both sweet and bitter flavors and possesses cooling properties. It helps to refresh the mind, enhance alertness and boost concentration. Tea can also promote body fluid production, quench the thirst, clear heat and phlegm and promote digestion and urination. Traditionally, it is used as:

A beverage to relieve indigestion and smooth bowel movements. It can also be used to relieve headaches, dizziness, heat stroke and sleepiness.

An antidote to clear toxic heat evils by promoting bowel movements and urination.

Many beneficial effects of tea have been attributed the strong antioxidative activities of its polyphenolic compounds. Modern studies have found that green tea contains a unique set of catechins, namely tea polyphenols, including (-)-epicatechin (EC), (-)-epicatechin-3-gallate (ECG), (-)-epigallocatechin (EGC) and (-)-epigallocatechin-3-gallate (EGCG). EGCG is considered the major component responsible for tea's antioxidant activity, anti-aging properties and cardiac health maintenance. 1

Effects of Green Tea in oxidative stress and cardiac health
Tea, especially green tea, is an important source of polyphenols, which act as strong antioxidants by scavenging reactive oxygen and nitrogen species and by chelating redox-active transition metal ions. 2 Green tea's beneficial effects are attributed to its ability to reduce oxidative stress, lipid peroxidation, free radical generation and unhealthy LDL cholesterol-oxidation. 3,4,5,6,7 There is also suggestive evidence that green tea catechins have a role in the protection against degenerative disorders. 8

Several oxidative stress conditions such as highly competitive physical exercise or pregnancy result in an increase of membrane-bound haemoglobin (MBH) due to the degradation of red blood cell metabolism and of the antioxidant defenses in aged and damaged red blood cells. A clinical study found that drinking green tea corresponds to a significant decease in MBH, suggesting a reduced oxidative stress within red blood cells. 9

Experimentally, some catechins have also been shown to inhibit a key enzyme (squalene epoxidase) in the pathway of cholesterol biosynthesis. 10 The potent antioxidant properties of tea polyphenols reduce free radical damage to cells and prevent the oxidation of LDL cholesterol. 11

Green Tea for Immune Health
There is evidence to suggest green tea may be beneficial in supporting immune health. Several in vitro studies found tea polyphenols inhibit a vast array of clinically relevant molecular targets and cellular processes such as antiapoptotic Bcl-2 proteins, 12 and vascular endothelial growth factor receptor (VEGFR) signaling. 13 There is further support by animal studies suggesting the consumption of green tea or green tea supplements with high levels of tea polyphenols may have a significant effect on the prevention of abnormal cell growth. 14

The health benefits of green tea are based on tradition or scientific theories. A number of pharmacological studies have demonstrated that the unique set of catechins in green tea possesses various biological activities in human body, such as antioxidant, immune system and cardiovascular system, which can potentially interfere with many disease-related biochemical processes. Green tea is a freely available phenomenal medicinal herb without a prescription and horrendous negative side effects. Hence, many people are turning to green tea to enhance their health and protect against chronic diseases.